1. Field of the Invention
The field of the invention is medicine, and more particularly, the effect of amylin antagonists and amylin blockers on glucose metabolism in peripheral tissues as a treatment for obesity and essential hypertension and associated lipid disorders and atherosclerosis.
2. Description of Related Art and Introduction of the Invention
Publications and other materials including patent applications used to illuminate the specification are incorporated herein by reference.
A 37-amino acid peptide called amylin has been isolated, purified, sequenced and characterized. The present invention discloses the use of amylin antagonists and amylin receptor blockers to control glucose and lipid metabolism for the treatment of obesity and essential hypertension and associated lipid abnormalities and atherosclerosis.
The peptide hormone amylin (previously termed "diabetes associated peptide") was isolated and characterized by Cooper et al. from the amyloid of the islets of Langerhans in Type 2 diabetics, and immunoreactivity to the peptide has been demonstrated in islet B-cells of both normal and Type 2 diabetic subjects. In view of our discovery that this hormone is derived from pancreatic amyloid masses, we have proposed the name "amylin".
Although it has been known for some time that amyloid masses in the islets of Langerhans are a feature of the pancreas in Type 2 diabetes, the monomer has only recently been shown to be the 37-amino acid peptide amylin (Cooper, G. J. S. et al., Proc. Natl. Acad. Sci. USA 1987; 84: 8628-8632), which has the following amino acid sequence: ##STR1## Specific immunoreactivity to amylin is found in islet amyloid, and in cells of the islets of Langerhans, where it co-localizes with insulin in the islet B-cells (see: Cooper, G. J. S. et al., Lancet ii: 966 (1987)). We have shown that the native amylin molecule contains a disulfide bridge between the Cys residues shown at positions 2 and 7 and is amidated at its 3' end. Both of these post-translational modifications are necessary for the complete biologic activity of amylin.
Insulin resistance is a major pathophysiological feature in both obese and non-obese type 2 diabetics, and was previously believed to be due mainly to a post-binding defect in insulin action (see: Berhanu et al., J. Clin. Endoc. Metab. 55: 1226-1230 (1982)). Such a defect could be due to an intrinsic property of peripheral cells, or caused by a change in concentration of a humoral factor in plasma, or both. Previous attempts at demonstrating a humoral factor responsible for insulin resistance have yielded conflicting results. Nor has it been possible to demonstrate an intrinsic post-binding defect in insulin resistance in type 2 diabetes mellitus (see: Howard, B. V. Diabetes 30: 562-567 (1981); Kolterman, O. G. et al., J. Clin. Invest.: 68: 957-969 (1981)).
The mechanisms of insulin resistance in type 2 diabetes are complex. Evidence, gleaned mainly from studies on adipose tissue, was said to suggest that in the mildest cases, insulin resistance could be accounted for largely by a deficiency in numbers of insulin receptors on peripheral target cells, but that as the degree of fasting hyperglycaemia increases, a post-receptor defect of insulin action emerges and progressively increases in significance (see: Kolterman et al., supra). The impaired glucose tolerance accompanying insulin resistance in type 2 diabetes is believed to be caused largely by decreased glucose uptake in perpheral tissues, but incomplete glucose-induced suppression of hepatic glucose production has also been said to be implicated (see: Wajngot et al., Proc. Natl. Acad. Sci. USA 70: 4432-4436 (1982)). In both obese and non-obese type 2 diabetics, the insulin dose-response curve is shifted to the right and there is a marked decrease in the maximal rate of glucose disposal and of total-body glucose metabolism in type 2 diabetics compared with non-diabetic subjects (Kolterman et al., supra; De Fronzo, R. A. et al., J. Clin. Invest. 76: 149-155 (1985)).
The majority of the glucose in an oral glucose load in humans is utilized in the periphery where, quantitatively, the most important tissue is skeletal muscle (De Fronzo, R. A. et al., J. Clin, Invest. 76: 149-155 (1985); Katz et al., Diabetes 32: 675-679 (1983)), and it has recently been shown that reduced clearance of glucose into skeletal muscle accounts for the bulk of the decrease in total body glucose uptake in type 2 diabetics (see: De Fronzo et al., supra). The in vivo decrease in insulin-mediated glucose disposal in type 2 diabetes is said to be caused mainly by a marked decrease in non-oxidized glucose storage, primarily in skeletal muscle, rather than by a major shift in glucose or lipid oxidation (Meyer et al., Diabetes 29: 752-756 (1980); Boden et al., Diabetes 32: 982-987 (1983)). The degree to which relative insulin deficiency contributes to the overall reduction in whole-body glucose clearance is unclear. Muscle glycogen synthesis has been shown to determine the in vivo insulin-mediated glucose disposal rate in humans (Bogardus et al., J. Clin. Invest. 73: 1185-1190 (1984)).
Weight gain requires an intake of energy that is greater than its expenditure. It therefore follows that obesity occurs in response to sustained caloric intake in excess of requirement. Food intake need not be abnormally high during the development of obesity, provided activity is limited, although the development of obesity is normally accompanied by a high caloric intake. Once attained, the obese state is commonly maintained at a level of caloric intake insufficient to produce obesity, said to happen because accompanying morbidity prevents exercise (Foster, D. W. In: Wilson, J. D. & Foster, D. W., eds. Williams Textbook of Endocrinology. 7th ed. Saunders, Philadelphia, 1985: 1081-1107).
Obese patients frequently claim that they gain weight on amounts of food that do not cause obesity in other persons, perhaps due to a more efficient use of ingested calories than would be the case in lean individuals Conversely, some persons can maintain weight near normal despite wide swings in the amount of food eaten (Black, D. et al., J.R. Coll. Phys. Lond. 1983; 17: 5-65). The excess calories necessary to gain weight vary considerably even among normal subjects; for example, in one study, individuals on a high fat diet required between 4703 and 8471 kcal/kg to gain 1 kg (Goldman, R. F. et al. In: Bray, G. A., ed. Obesity in perspective. DHEW Publication No. (NIH) 75-708. Washington, D.C.: U.S. Government Printing Office, 1975: 165-186). Numerous experimental findings support a difference in metabolic efficiency between lean and obese, the former apparently having the ability to waste calories as heat not shared by the latter. Observations in genetically obese rodents also support this notion, as these rodents have a defect in theromoregulation on exposure to cold (Trayhurn, P. et al. Theromoregulation in genetically obese rodents: the relationship to metabolic efficiency. In: Festing, M. W. F., ed. Animal Models of Obesity. New York: Oxford University Press, 1979: 191-203). Since ingested energy can be utilized for work, heat generation, or energy storage, it follows that the greater the conversion of excess calories to heat, the lesser will be their availability for storage as fat, given a fixed requirement for work.
On the basis of animal studies, it has been proposed that the propensity to develop obesity is genetically influenced through alterations in thermogenic capacity (James, W. P. T. & Trayhurn, P. Lancet 1976; 2: 770-773; James, W. P. T. & Trayhurn, P. Br. Med. Bull. 1981; 37: 43-48; Coleman, D. L. Nutr. Rev. 1978; 36: 129-132). The idea is that, in the past, when food supply was intermittent, genetic pressure would favor an efficient metabolism, so that a high percentage of food eaten would be stored for periods when food was not available. This genetic property would then manifest as obesity when food was constantly available.
Experimental evidence for this theory has been provided by experiments with the children of obese parents, which were based on the observation that obese children frequently have obese parents. Numerous metabolic indices indicated that the children of the obese have more efficient metabolisms, and that, early on, they may control their weight by restricting their food intake (i.e. eating physiologically) (Griffiths, M. & Payne, P. R. Nature 1976; 260: 698-700). In persons with established obesity, it has been said that there is probably a defect in glucose-induced (post prandial) theromogenesis, presumably as a result of insulin-resistance, but the defect is relatively small (Golay, A. et al., Diabetes 1982; 31: 1023-1028).
Hypertension, obesity and glucose intolerance (impaired glucose tolerance and type 2 diabetes mellitus) are associated in both clinical and epidemiological studies (Chiang et al., Circulation 39: 403-421 (1960); Sims, E. A. H. Hypertension 4 (Suppl. 3); 43-49 (1982); Bray, G. A. Dis. Mon. 26: 1-85 (1979); West, K. M. Epidemiology of Diabetes and its Vascular Lesions. Elsevier/North Holland, New York, pp. 191-284, 351-389 (1978); Medalie et al., Arch. Int. Med. 135: 811-817 (1975); Zimmett, P. Diabetologia 22: 399-411 (1982); Barrett-Connor, AM. J. Epidemiol. 113: 276-284 (1981); Jarrett et al., Int. J. Epidemiol., 7: 15-24 (1978); Butler et al., Am. J. Epidemiol. 16, 971-980 (1982) and may have common pathogenetic mechanisms (Modan et al., J. Clin. Invest. 75: 809-817 (1985)).
There are two major and distinct syndromes of hypertension in diabetes mellitus, essential hypertension and hypertension accompanying diabetic nephropathy (see respectively: Sleight, P. Essential Hypertension. In: The Oxford Textbook of Medicine. Weatherall, D. J. et al., eds. Oxford University Press, Oxford (1987); Magili et al., N. Engl. J .Med. 318: 146-150 (1988)). Over 50% of patients presenting clinically with type 2 diabetes mellitus have essential hypertension, i.e. elevated arterial blood pressure not secondary to an established primary cause of hypertension. Essential hypertension should be distinguished from the hypertension that frequently develops during the course of type 1 and type 2 diabetes, which is usually related to the onset and progression of diabetic nephropathy, and is therefore a secondary, renal form of hypertension, although the possibility of an inherited predisposition to raised arterial pressure in this condition has also been suggested (Magili et al , supra). The latter form of hypertension is accompanied by biochemical evidence of progressive nephropathy (i.e. microalbuminuria, elevated serum creatinine, etc.) and can thus be distinguished from essential hypertension not accompanied by nephropathy.
Insulin resistance is a major feature common to essential hypertension, obesity and type 2 diabetes. This insulin resistance occurs primarily in skeletal muscle, and results mainly from depressed rates of glycogen synthesis (non-oxidative glucose storage). Recent evidence confirms that essential hypertension is an insulin resistant state (Ferrannini et al., N. Engl. J. Med. 317: 350-357 (1987); Shen, D. C. et al., J. Clin. Endoc. Metab. 1988: 580-583 (1988)). The insulin resistance involves glucose but not lipid or potassium metabolism, is located in peripheral tissues, is limited to nonoxidative pathways of intracellular glucose disposal (primarily glycogen synthesis), and is directly correlated with the severity of the hypertension. It has also been demonstrated that the bulk (more than 70%) of glucose uptake in the whole body occurs in skeletal muscle (De Fronzo, R. A. & Ferrannini, E. Diabetes Metabolism Reviews 3: 415-459 (1987)). In type 2 diabetes, it is primarily insulin resistance in skeletal muscle that is said to account for the low rates of glucose clearance from the blood and, hence, to be a major determinant of impaired glucose tolerance (Kolterman, O. G. Diabetes/Metabolism Reviews 3: 399-414 (1987)). Therefore, a major common feature between essential hypertension, type 2 diabetes mellitus and obesity is insulin resistance in skeletal muscle. While we believe that elevated amylin levels are the cause of this insulin resistance in type 2 diabetes, it is our further determination that they also contribute to the disease state in essential hypertension and obesity.